'\" et
.TH SLEEP "1P" 2017 "IEEE/The Open Group" "POSIX Programmer's Manual"
.\"
.SH PROLOG
This manual page is part of the POSIX Programmer's Manual.
The Linux implementation of this interface may differ (consult
the corresponding Linux manual page for details of Linux behavior),
or the interface may not be implemented on Linux.
.\"
.SH NAME
sleep
\(em suspend execution for an interval
.SH SYNOPSIS
.LP
.nf
sleep \fItime\fR
.fi
.SH DESCRIPTION
The
.IR sleep
utility shall suspend execution for at least the integral number of
seconds specified by the
.IR time
operand.
.SH OPTIONS
None.
.SH OPERANDS
The following operand shall be supported:
.IP "\fItime\fR" 10
A non-negative decimal integer specifying the number of seconds for
which to suspend execution.
.SH STDIN
Not used.
.SH "INPUT FILES"
None.
.SH "ENVIRONMENT VARIABLES"
The following environment variables shall affect the execution of
.IR sleep :
.IP "\fILANG\fP" 10
Provide a default value for the internationalization variables that are
unset or null. (See the Base Definitions volume of POSIX.1\(hy2017,
.IR "Section 8.2" ", " "Internationalization Variables"
for the precedence of internationalization variables used to determine
the values of locale categories.)
.IP "\fILC_ALL\fP" 10
If set to a non-empty string value, override the values of all the
other internationalization variables.
.IP "\fILC_CTYPE\fP" 10
Determine the locale for the interpretation of sequences of bytes of
text data as characters (for example, single-byte as opposed to
multi-byte characters in arguments).
.IP "\fILC_MESSAGES\fP" 10
.br
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard error.
.IP "\fINLSPATH\fP" 10
Determine the location of message catalogs for the processing of
.IR LC_MESSAGES .
.SH "ASYNCHRONOUS EVENTS"
If the
.IR sleep
utility receives a SIGALRM signal, one of the following actions shall
be taken:
.IP " 1." 4
Terminate normally with a zero exit status.
.IP " 2." 4
Effectively ignore the signal.
.IP " 3." 4
Provide the default behavior for signals described in the ASYNCHRONOUS
EVENTS section of
.IR "Section 1.4" ", " "Utility Description Defaults".
This could include terminating with a non-zero exit status.
.P
The
.IR sleep
utility shall take the standard action for all other signals.
.SH STDOUT
Not used.
.SH STDERR
The standard error shall be used only for diagnostic messages.
.SH "OUTPUT FILES"
None.
.SH "EXTENDED DESCRIPTION"
None.
.SH "EXIT STATUS"
The following exit values shall be returned:
.IP "\00" 6
The execution was successfully suspended for at least
.IR time
seconds, or a SIGALRM signal was received. See the ASYNCHRONOUS EVENTS
section.
.IP >0 6
An error occurred.
.SH "CONSEQUENCES OF ERRORS"
Default.
.LP
.IR "The following sections are informative."
.SH "APPLICATION USAGE"
None.
.SH EXAMPLES
The
.IR sleep
utility can be used to execute a command after a certain amount of
time, as in:
.sp
.RS 4
.nf

(sleep 105; \fIcommand\fP) &
.fi
.P
.RE
.P
or to execute a command every so often, as in:
.sp
.RS 4
.nf

while true
do
    \fIcommand\fP
    sleep 37
done
.fi
.P
.RE
.SH RATIONALE
The exit status is allowed to be zero when
.IR sleep
is interrupted by the SIGALRM signal because most implementations of
this utility rely on the arrival of that signal to notify them that the
requested finishing time has been successfully attained. Such
implementations thus do not distinguish this situation from the
successful completion case. Other implementations are allowed to catch
the signal and go back to sleep until the requested time expires or to
provide the normal signal termination procedures.
.P
As with all other utilities that take integral operands and do not
specify subranges of allowed values,
.IR sleep
is required by this volume of POSIX.1\(hy2017 to deal with
.IR time
requests of up to 2\|147\|483\|647 seconds. This may mean that some
implementations have to make multiple calls to the delay mechanism of
the underlying operating system if its argument range is less than
this.
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fIwait\fR\^"
.P
The Base Definitions volume of POSIX.1\(hy2017,
.IR "Chapter 8" ", " "Environment Variables"
.P
The System Interfaces volume of POSIX.1\(hy2017,
.IR "\fIalarm\fR\^(\|)",
.IR "\fIsleep\fR\^(\|)"
.\"
.SH COPYRIGHT
Portions of this text are reprinted and reproduced in electronic form
from IEEE Std 1003.1-2017, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, 2018 Edition,
Copyright (C) 2018 by the Institute of
Electrical and Electronics Engineers, Inc and The Open Group.
In the event of any discrepancy between this version and the original IEEE and
The Open Group Standard, the original IEEE and The Open Group Standard
is the referee document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
.PP
Any typographical or formatting errors that appear
in this page are most likely
to have been introduced during the conversion of the source files to
man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
